Ionic variability in the hydrographic network of Oaxaca, Mexico: multivariate graphic and statistical alternative

Abstract

Background. Factors such as lithology, geomorphology, climate and anthropogenic activities, cause ionic variability of surface, subsurface and underground water. The study of this variability allows to know its hydrochemical characteristics for its subsequent use. The interpretation of the ionic variability is carried out by mean of graphic methods, and multivariate statistics have been integrated into these analyses during the last few years. Objective. To perform a chemical analysis, to identify the factors affecting the water, and to prove that complementing the Piper diagram with a multivariate analysis helps to obtain a better interpretation of results. Methods. This work was carried out in the Oaxaca-Puebla hydrographic network, considering the complex relief and the heterogeneous lithological and climate conditions, especially in Oaxaca. A total of 90 samples were collected, three of which were taken in salt flats in Zapotitlán, Puebla and the rest of them in the state of Oaxaca. A Piper diagram was used for water classification, as well as the principal component analysis (PCA) to improve the interpretation of data. Results. The triangular diagram allowed to classify the waters of the hydrographic network into two large groups, calcium-magnesium bicarbonate, and calcium-magnesium sulfate, in addition to the separation of saline waters. The PCA, in addition to showing the same groups of waters, allowed to prove a higher concentration of sodium chloride at the highest point of the salt flat, as compared to the other two that were taken at this site. With the PCA, the water of the Copalita river basin could be classified as calcium-magnesium bicarbonate, coinciding with previous studies. Conclusions. By complementing a Piper diagram with a PCA, the interpretation of the ionic variability of the Oaxaca-Puebla hydrographic network improved.